The process of dividing a network into 2/more networks is called subnetting. A subnet is a logical sub-division of an IP address.
Subnetting reduces network congestion and improves network performance.
Let’s take an example - your supervisor wants comes to you and says, “Here is the network ID 192.168.4.0/24. Please create 3 subnets for the office, the front desk and one for public use.”
The task is to list down - the number of usable host IDs, network IDs, subnet mask, host ID range, and broadcast ID.
- Step 1 - Select a number from row 1 which is equal to or just greater than the number of subnets required. We choose 4.
- Step 2 - Select the whole column i.e. Subnets-4, Host-64, Mask-/26. We choose 4 subnets, each of which will have 64 host IDs including networking ID and broadcasting ID, and /26 is the subnet mask for all of these subnets.
Let’s find the first network ID which is always the original network ID, i.e. 192.168.4.0
The second network ID can be obtained by simply adding 64 (the number of hosts) to the first network ID, 192.168.4.64
Similarly, third network ID becomes 192.168.4.128 and fourth network ID becomes 192.168.4.192
The subnet mask becomes /26 as per the column we selected.
# of usable Host IDs
As per the selected column, the number of hosts becomes 64, however, the first and last host IDs are reserved for network ID and broadcast ID. Thus, the net usable IDs come down to 64–2 = 62 for all the subnets.
Since, the last host ID is reserved for broadcast ID, the broadcast ID for first subnet becomes 192.168.4.63 the broadcast ID for second subnet becomes 192.168.4.127 the broadcast ID for third subnet becomes 192.168.4.191 the broadcast ID for fourth subnet becomes 192.168.4.255
Host ID range
The range of host IDs refers to the host IDs between the network ID and the broadcast ID in a subnet.
You can assign any ¾ subnets to the use cases - office, front-desk, public use. The only downside is that one of these 4 subnets will be wasted.